This invention relates to a center section for use in a hydrostatic transmission (“HST”) or an integrated hydrostatic transaxle (“IHT”).
The invention disclosed herein is an improved center section for use in an IHT or an HST, where the center section is of a two-piece design. Center sections containing hydraulic porting for connecting a rotating hydraulic pump and motor are known in the art and are disclosed in, e.g., commonly owned U.S. Pat. Nos. 5,314,387 and 6,122,996, the terms of which are incorporated herein by reference.
Two-piece center sections for use in an IHT are also known. For example, different two-piece center section designs are disclosed in the file history for U.S. Pat. No. 5,505,279 and other patents claiming priority from U.S. Pat. No. 4,903,545. These designs included two separate pieces, one for the motor running surface and one for the pump running surface, and the two pieces were bolted together at a right angle to one another for insertion into an integrated hydrostatic transaxle housing. Two of these known prior art designs are shown in FIGS. 12–15.
The first prior art design in FIGS. 12 and 13 shows a two piece center section 120 having a pump portion 130 and a motor portion 132 bolted together by two bolts 134. Separate openings 180 are shown for bolting center section 120 into an integrated hydrostatic transaxle such as that shown in U.S. Pat. No. 4,903,545. Pump kidneys 143 and motor kidneys 142 are hydraulically connected via porting 160 to connect the hydraulic pump cylinder block and motor cylinder block (not shown) of the integrated hydrostatic transaxle.
FIGS. 14 and 15 show a similar but slightly different two piece center section 220 where pump portion 230 is bolted to motor portion 232 by bolts 234. Again, hydrostatic porting 260 is formed therein to connect pump kidneys 243 and motor kidneys 242. Separate fasteners (not shown) are needed to secure two piece center section 230 to the transaxle housing via openings 280. It is understood that the pump portions and motor portions in both of these prior art designs can be reversed.